I will try it too. Perhaps you're right. But, I don't see any reason why it wouldn't work.
We have a note-on midi message with velocity information. This message comes from a DAW, another Keyboard, the internal keyboard, the Sequencer and so on.
Whatever note-on source, the same information is transmitted : channel, note number, velocity.
Whatever synth engine, it receives this message. When you change your velocity on the keyboard you send the same message on midi channel, that way, you trigger different samples inside the HD-1. So, I don't see why you shouldn't get the same result.

But I will try. Not hard to do : one HD-1 program with 2 samples in layers , placed on one track of the Seq. Recording just one bar 2 times the same note ; going to MIDI event edit and modify the velocity value of the second note according to the inital HD-1 layer. I will see if it works or not.

Modifying velocity inside the track, different samples are triggered. And so, it responds well to Midi velocity Control. That way you can trigger any sample you want, as you would do with the keyboard itself.